1. Field of the Invention
This invention relates generally to a slide fastener and has particular reference to a fastener stringer having a continuous plastic filament spirally formed and woven simultaneously into a longitudinal edge of a stringer tape.
2. Prior Art
There have been proposed a number of slide fasteners or zippers of the type described, which comprise a woven stringer tape and a plastic filament woven into a longitudinal edge of the tape, the filament being usually formed into a helical coil structure composed of a succession of loops or elongated convolutions each having a coupling head, an upper and a lower leg and a connecting portion.
When bent into such helical coil formation, the filament which is thicker and harder than the weave yarn tends to yield back, thereby causing the fastener stringer to stretch longitudinally and the filament loops to tilt away from an upright posture with respect to the plane of the stringer tape. This displacement of the filament loops would result in irregular pitch of the filament loops, which in turn hinders smooth closing and opening operation of the slide fastener.
A woven slide fastener stringer is exemplified in DE 3347067 which is aimed at eliminating or alleviating the above noted drawbacks of the conventional stringers and which comprises a weave system for affixing a row of coupling elements to and along a longitudinal edge of each of two companion support tapes, the weave system essentially comprising supplemental warp yarns running in a manner similar to lower binding warp yarns and extending substantially linearly under the lower surface of a lower leg portion of each coupling element and tightening warp yarns extending, similarly to upper binding warp yarns, alternately over and under two adjacent coupling elements. The tightening warp yarns are intended to bring the upper and lower leg portions of the coupling elements closely together and at the same time to urge laid-in weft yarns intimately against the lower leg portions of the elements. This prior woven stringer device however has the difficulty that when enough tension is applied to the tightening warp yarns to held the coupling elements firmly in place, this would cause disturbance or malalignment of adjacent elements or irregularities in the element-to-element interspace or pitch and therefore, a compromise is required in the amount of tension to the weave system such that the coupling elements tend to shift out of the proper operative posture.
Another prior woven stringer is introduced in Japanese Utility Model Publication No. 1-37441 in which a plurality of binding warp yarns are provided in parallel with each other both over the upper legs and under the lower legs of a row of coupling elements, and gap-filling or tightening yarns are interwoven with weft yarns extending over the upper legs and under the lower legs of the elements. A drawback of this prior device is that the weft yarns interposed between the upper legs of adjacent elements are apt to interfere with the tightening warp yarns, resulting in a reduction in the tension required to pull the element legs together and also to adhere the weft yarns to the lower legs of the elements.